Since the discovery of efferent innervation of the vestibular system in the cat twenty-nine years ago, there has been an active interest in elucidating the action of efferent neurons on their peripheral targets and the behavioral significance of efferent activation. The octavolateralis efferent system of fishes has many features which make it particularly attractive to study including: 1) the ability to intracellularly record from primary afferent fibers peripherally and efferent somata within the central nervous system; 2) the ability to stimulate efferent neurons independently of afferents; and 3) the ability to relate efferent activity to particular behaviors. Although the morphological organization of the octavolateralis efferent system has been extensively studied in fishes, few studies have analyzed the physiological interactions between efferent neurons and neurons within the central nervous system (CNS). We propose to study efferent neurons of the goldfish and their physiological relationship to cranial relay neurons and the goldfish Mauthner cell. specifically, we propose to simultaneously record intracellularly from the Mauthner axon or cranial relay neurons and efferent somata in an attempt to decipher the circuitry involved in the suppression of afferent activity before and firing the Mauthner cell initiated startle response. Intracellular injections of horseradish peroxidase in conjunction with the physiological studies will allow an analysis of the morphological pathways involved. Our proposed studies are designed to provide information about the interactions between efferent neurons and CNS neurons with the ultimate goal of better understanding how the efferent octavolateralis system is involved in specific behaviors.